The present invention relates generally to sealing assemblies for rotary machines and, more particularly, to a sealing assembly for a steam or gas turbine.
Rotary machines include, without limitation, steam turbines, compressors, and gas turbines. A steam turbine has a steam path that typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path, which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor, and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
To reduce gas and steam-path leakage in gas and steam turbine engines, sealing assemblies are used. In various types of turbine sealing assemblies, rotor groove sealing strips are disposed between rotary and stationary components of the turbine engine. Presently, the rotor groove sealing strips are peened using a variety of methods. One method includes, but is not limited to, grinding a curved tip on a hand chisel that is impacted by a hand held hammer to deform or peen wire in a groove. Another method includes grinding a curved tip in a hand held pneumatic vibratory hammer to peen caulk wire into the groove. The current methods of peening the caulk wire, however, do not consistently achieve a high pull out strength of a rotor groove seal created by the peened caulk wire.
Maximizing the pull out strength of the rotor groove seal is important because the rotor groove seal experiences several pullout forces during operation of the turbine. Such forces include, but are not limited to, a centrifugal pull out force, a moment force at the base of the seal due to steam pressures, and radial and tangential forces during metal-to-metal rub, as well as rub against abradable type coatings intentionally applied to a housing defining the steam path. It is therefore desirable to have a rotor groove seal with a predictably high pull out strength.
Additionally, the current methods of peening the caulk wire result in unrepeatable peening such that this peening causes unpredictable seal pull out strengths. The wide variance in seal pull out strengths is due to a variety of factors including, but not limited to, improper positioning of the peening tool by the operator and inconsistent forces applied with the peening tool. For example, the standard deviation of the seal pull out strengths produced by hand peening can be as large as 200 pounds in a population that has a mean seal pull out strength of 600 pounds. The wide variance in seal pull out strength is problematic because low seal pull out strengths can result in seals coming loose during operation and result in significant damage to the turbine including down time of the same.
Accordingly, it would be desirable to develop a cost effective sealing method and apparatus that can produce rotor groove seals having a predictable seal pull out strength, without impairing the performance of the sealing strips.